Mariana Sanchez, Al Jazeera's correspondent in Caracas, said that the protests had been largely peaceful.

She said: "Earlier a group of students who favour President Hugo Chavez approached the other students at the central university and police had to throw some tear gas at them ... but mainly it has been a very peaceful march."

The students handed a document to the attorney general asking for freedom of expression, respect for democracy, respect for the autonomous status of the universities and RCTV's licence to be renewed, she said.

Chavez began the news conference with a recording of the heated debate between his foreign minister and Condoleezza Rice, the US secretary of state, at an Organisation of American States (OAS) meeting in Panama on Tuesday.

'Great defeat'

The OAS declined to adopt a US request to investigate the removal of Radio Caracas Television from free-to-air television.

Chavez described the decision as "a great defeat for the empire.

"It was the greatest defeat - a moral defeat, a political defeat."

Riot police used tear gas to break up rival groups of students [AFP]

In the video of the OAS meeting, Nicolas Maduro, the foreign minister, demanded that the OAS investigate human rights violations at the US prison at Guantanamo Bay and on the US-Mexico border before Rice walked out.

"She was trying to maintain her calm, but already from the beginning you could tell she was a little annoyed," Chavez said.

"I know her very well and I know when she's annoyed ... surely because they couldn't find anyone to do their work, their dirty work, and she had to leave."

Chavez has said he will not go back on his refusal to renew the licence of RCTV, which he accuses of a key role in backing a short-lived 2002 coup against him.

Some of RCTV's programmes are still making their way to viewers on the internet or by satellite.

Other shows reach no audience at all, but actors, cameramen and sound engineers continue to produce them in the hope they may one day be seen.